0AD has generted more excitement in the RTS space, for me, than the initial release of 'The Ancient Art of War'.
Try it out, if just for the late-game seige engines.
[Wikipedia 0AD](https://en.wikipedia.org/wiki/0_A.D.\_(video_game))
[Trailer video](https://www.youtube.com/watch?v=3MhcRPm7Zhg)